The present exemplary embodiment relates to a method of forming ultrafine, high purity calcium lanthanoid (e.g., La,Gd) sulfide powders. The powders find particular application in the formation of transparent ceramic materials with high mechanical strength for Long Wave Infrared (LWIR) sensor windows, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
Sensor systems for Long Wave Infrared (LWIR) that operate in the 8-12 μm range find application in armored transportation, air and naval vehicles, and in industrial control applications, among others. Such sensors may employ detectors based on mercury cadmium telluride (MCT) for detecting LWIR or MWIR (3-5 μm) radiation. The sensor is protected from the surrounding environment by an infrared-permeable window. Currently, windows are formed from single crystal ZnS, ZnSe and Ge. These materials suffer from various limitations. ZnS and ZnSe are soft materials and have poor environmental weatherability. Ge has poor strength, a high absorption coefficient, and becomes opaque at temperatures above 100° C.
Ceramic polycrystalline materials can be produced which have higher strength than conventional single crystal materials. However, such materials are generally poorly transparent in the LWIR range.
There remains a need for materials which are less susceptible to environmental problems for use in a variety of LWIR applications.